Optically active materials

ABSTRACT

A compound is of formula (I), in which: A 1  to A 4 , E 1  and E 2  each independently represent hydrogen or an optionally-substituted hydrocarbon group; B 1  and B 2  each independently represent a single bond, an oxygen atom or an optionally-substituted hydrocarbon group; MG 1  and MG 2  each independently represent an optionally-substituted ring system; CG is a divalent or polyvalent chiral group. The optically active compound may be used as a doping agent for liquid crystals for a wide range of applications including solid state cholesteric filters for projection displays, circular polarisers, optical filters, etc.

This application is a national stage filing under 35 U.S.C. § 371 ofinternational application no. PCT/CH00/00673, filed on Dec. 20, 2000.This application claims the benefit of priority under 35 U.S.C. § 119(a)to GB patent application no. 9930557.5, filed on Dec. 23, 1999 and EPpatent application no. 99310561.8, filed on Dec. 23, 1999.

This invention relates to optically active materials and their use asdoping agents for liquid crystals for a wide range of applicationsincluding solid state cholesteric filters for projection displays,circular polarisers, optical filters, etc.

The addition of an optically-active compound to a non-optically-activeliquid crystalline phase is one of procedures used for the conversion ofnon-optically-active into optically-active mesophases. The nematicphase, for example, is converted to the cholesteric one when being dopedwith a small amount of an optically-active substance. This conversionmanifests itself by the occurrence of an intermolecular helix which ischaracterised by the so-called helical twisting power (HTP) given inEquation 1: $\begin{matrix}{{H\quad T\quad P} = {{{\frac{\mathbb{d}p^{- 1}}{\mathbb{d}x}}_{x = 0} \cong \frac{p^{- 1}}{x}} = {\sum\limits_{i}{x_{i}\left( {H\quad T\quad P} \right)}_{i}}}} & (1)\end{matrix}$

-   -   HTP(μm⁻¹) helical twisting power for small concentrations    -   p(μm) pitch of induced helix, + for (P)-helix, − for (M)-helix    -   x mole fraction of the dopant    -   _(i) sum over all optically-active conformers of the dopant    -   x_(i) mole fraction of conformer i

Said HTP is in fact a measure for the efficiency of a given dopant andis determined by the Cano method with solutions of the dopant in thehost mesophase. Since the optically-active guest and thenon-optically-active host compounds are not necessarily compatible atthe molecular scale, their binary solution is frequently characterisedby undesirable changes of the thermotropic sequence of the initial hostliquid crystalline material, like for example a depression of theclearing point. Those changes could in turn have negative effects on thephase properties of the host, such as a decrease of the birefringenceetc. Therefore, an optically-active dopant is sought so that with verysmall concentrations of this latter, large values of HTP could beinduced.

As such efficient optically-active dopants there are the binaphtholderivatives described in GB-A-2 298 202. However optically-activebinaphthol derivatives may undergo partial racemisation when beingheated. Besides, their preparation is expensive because it includesasymmetric resolution of binaphthol racemate as a crucial reaction step.

Other classes of optically active dopants which are of easier chemicalaccess than binaphthol derivatives are those described in U.S. Pat. No.5,780,629, which are consisting of compounds having at least onedivalent or polyvalent chiral group and at least one mesogenic group.Based on this molecular architecture, in which the chiral group ispresent at peripheral position of the mesogenic cores, we have preparedsome chiral dimesogenic derivatives. Nevertheless, their use as dopingagents for liquid crystals has only provided mixtures with a relativelysmall HTP. However, we have now discovered that a further class ofcompounds, including within its scope compounds that exhibit a chiralgroup at lateral position is of at least two rod-like shaped organicresidues, is efficient for producing a large HTP. Besides, theirsynthesis is trivial and inexpensive since they are obtained in fewreaction steps starting from commercially available optically activeresidues.

Thus, the invention provides chiral “sandwich” derivatives of formula I:

in which

-   A¹ to A⁴ each independently represent hydrogen; an    optionally-substituted methyl group; or an optionally-substituted    hydrocarbon group of 2 to 80 C-atoms, in which one or more C-atoms    may be replaced by a heteroatom, in such a way that oxygen atoms are    not linked to one another;-   E¹ and E² each independently represent hydrogen; an    optionally-substituted methyl group; or an optionally-substituted    hydrocarbon group of 2 to 80 C-atoms, in which one or more C-atoms    may be replaced by a heteroatom, in such a way that oxygen atoms are    not linked to one another;-   B¹ and B² each independently represent a single bond, an oxygen atom    or an optionally-substituted hydrocarbon group of 1 to 80 C-atoms,    in which one or more C-atoms may be replaced by a heteroatom, in    such a way that oxygen atoms are not linked to one another;-   MG¹ and MG² each independently represent an optionally-substituted    aromatic or non-aromatic carbocyclic or heterocyclic rings system,    with 1 to 80 C-atoms;-   CG is a divalent or polyvalent chiral croup derived, in particular,    from sugars; from optically active biaryls such as optionally    substituted binaphthyl or optionally substituted biphenyl; or from    bifunctional or polyfunctional compounds such as optically active    alcohols, glycols or amino acids; and-   n1 and n2 are each independently 1 or 2, where “n1=2” (or “n2=2”)    indicates the presence of two separate linkages via the groups B¹    (or the groups B²) between the groups MG¹ and CG (or CG and MG²);    and in which further the substructures A¹-MG¹-A² and A³-MG²-A⁴ each    have a longitudinal axis and are linked lateral to the said    longitudinal axis to B¹ and B², respectively.

One possibility to form a longitudinal axis in the substructuresA¹-MG¹-A² and A³-MG²-A⁴ are compounds where two or more rings or a fusedring system are present in MG¹ or MG². Another possibility are compoundswhere at least one of A¹ or A² and A³ or A⁴ is different from hydrogen.

The compounds of the present invention are efficient for producing alarge HTP.

Their synthesis is trivial and inexpensive since they are obtained infew reaction steps starting from commercially available optically activeresidues.

They are compatible with liquid-crystalline compounds orliquid-crystalline mixtures (no significant change of the clearingtemperatures when used as dopants in a liquid-crystalline matrix).

They induce a large supercooling effect at the liquid-crystalline statewhen used as dopants in liquid-crystalline matrix hence avoidingcrystallisation problems during the manufacture of cholesteric films.

They may be used as doping agents for liquid crystals for a wide rangeof applications including solid state cholesteric filters for projectiondisplays, circular polarisers, optical filters, etc.

Preferred compounds of the present invention are those belonging toformula (I), in which:n1=n2=1.

Preferably at least one of A¹ to A⁴, E¹ and E² includes a polymerisablegroup, and each independently may be selected from formula (II):P-(Sp¹)_(k1)-(X′)_(t1)-  (II)wherein:

-   P is hydrogen or a polymerisable group selected from groups    comprising CH₂═CW—, CH₂═CW—O—, CH₂═CW—COO—, CH₂═C(Ph)-COO—,    CH₂CH—COO-Ph-, CH₂CW—CO—NH—, CH₂═C(Ph)-CONH—, CH₂═C(COOR′)—CH₂—COO—,    CH₂═CH—O—, CH₂═CH—OOC—, (Ph)—CH═CH—, CH₃CH═N—(CH₂)_(m3), HO—, HS—,    HO—(CH₂)_(m3)—, HS—(CH₂)_(m3)—, HO(CH₂)_(m3)COO—, HS(CH₂)_(m3)COO—,    HWN—, HOC(O)—, CH₂═CH-Ph-(O)_(m4),    wherein:    -   W represents H, F, Cl, Br or I or a C₁₋₅ alkyl group;    -   m3 is an integer having a value of from 1 to 9;    -   m4 is an integer having a value of 0 or 1,    -   R′ represents a C₁₋₅ alkyl group; and    -   R″ represents a C₁₋₅ alkyl group, methoxy, cyano, F, Cl, Br or        I;-   Sp¹ represents an optionally-substituted C₁₋₂₀ alkylene group, in    which one or more C-atoms may be replaced by a heteroatom;-   k¹ is an integer having a value of from 0 to 4;-   X¹ represents —O—, —S—, —NH—, N(CH₃)—, —CH₂(OH)—, —CO—, —CH(CO)—,    —SO—, —CH₂(SO)—, —SO₂—, —CH₂(SO₂)—, —COO—, —OCO—, —OCO—O—, —S—CO—,    —CO—S—, —SOO—, —OSO—, —SOS—, —CH₂—CH₂—, —OCH₂—, —CH₂O—, —CH═CH—, or    —C≡C—; and-   t¹ is an integer having a value of 0 or 1.

In relation to the residue of formula (II), the term Ph is to beunderstood as denoting phenylene and (Ph) as denoting phenyl.

The C₁₋₂₀ alkylene group Sp¹ may comprise branched or straight chainalkylene groups and may be unsubstituted, mono- or polysubstituted by F,Cl, Br, I or CN. Alternatively or in addition one or more of CH₂ groupspresent in the hydrocarbon chain may be replaced, independently, by oneor more groups selected from —O—, —S—, —NH—, N(CH₃)—, —CH(OH)—, —CO—,—CH₂(CO)—, —SO—, —CH₂(SO)—, —SO₂—, —CH₂(SO₂)—, —COO—, —OCO—, —OCO—O—,—S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—, —C≡C—, —(CF₂)—_(r), —(CD₂)_(s)— orC(W¹)═C(W²)—, with the proviso that no two oxygen atoms are directlylinked to each other. W¹ and W² each represent, independently, H,H—(CH₂)_(q1)— or Cl. The integers r, s and q1 each independentlyrepresent a number of between 1 and 15.

More preferably, A¹ to A⁴ and E¹ to E² each independently represent agroup of formula (III):P²-Sp⁵-X⁴—  (III)wherein:

-   P² represents hydrogen, CH₂═CW⁵— or CH₂═CW⁵—(CO)_(v2)O—,    -   wherein:    -   W⁵ represents H, CH₃, F, Cl, Br or I; and    -   v2 is 0 or 1,    -   R′ represents a C₁₋₅ alkyl group; and    -   R″ represents a C₁₋₅ alkyl group, methoxy, cyano, F, Cl, Br or        I;-   Sp⁵ represents a C₁₋₂₀ straight-chain alkylene group, especially    ethylene, propylene, butylene, pentylene, hexylene, heptylene,    octylene, nonylene, decylene, undecylene, or dodecylene; and-   X⁴ represents —O—, —CO—, —COO—, —OCO—, —C≡C—, or a single bond,    especially —O—, —COO—, —OCO— or single bond.

One or more of A¹ to A⁴ and E¹ to E² may also represent a C₁-C₂₀-alkyl,C₁-C₂₀-alkoxy, C₁-C₂₀-alkoxycarbonyl, C₁-C₂₀-alkylcarbonyl orC₁-C₂₀-alkylcarbonyloxy group, for example methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy,ethoxy, n-propoxy, isopropoxy, butoxy, pentyloxy, hexyloxy, heptyloxy,octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, methoxycarbonyl,ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl,hexyloxycarbonyl, octyloxycarbonyl, nonyloxycarbonyl, decyloxycarbonyl,undecyloxycarbonyl, dodecyloxycarbonyl, acetyl, propionyl, butyryl,valeryl, hexanoyl, heptanoyl, octanoyl, nonanoyl, decanoyl, undecanoyl,dodecanoyl, terdecanoyl, acetoxy, propionyloxy, butyryloxy, valeryloxy,hexanoyloxy, heptanoyloxy, octanoyloxy, nonanoyloxy, decanoyloxy,undecanoyloxy, dodecanoyloxy, terdecanoyloxy and the like.

In a second preferred embodiment of the present invention each or eitherof the groups B¹ and/or B² comprises a group of formula (IV):(X²)_(t2)-(Sp²)_(k2)-(X³)_(t3)  (IV)wherein:

-   Sp² represents a C₁₋₂₀ alkylene group;-   X² and X³ each independently represent —O—, —S—, —NH—, N(CH₃)—,    —CH(OH)—, —CO—, —CH₂(CO)—, —SO—, —CH₂(SO)—, —SO₂—, —CH₂(SO₂)—,    —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—,    —CH₂—CH₂—, —OCH₂—, —CH₂O—, —CH═CH—, —C≡C— or a single bond;-   k² is an integer, having a value of 0 or 1; and-   t² and t³ are integers, each independently having a value of 0 or 1;    with the proviso that oxygen atoms are not linked one to another.

Preferably B¹ and B² each independently represent a group of formula(IV), wherein:

-   X² to X³ each independently represent —O—, —CO—, —COO—, —OCO—,    —C≡C—, or a single bond, especially —O—, —COO—, —OCO— or a single    bond; and-   Sp² represents a C₁₋₂₀ straight-chain alkylene group, especially    ethylene. propylene, butylene, pentylene, hexylene, heptylene,    octylene, nonylene. decylene, undecylene or dodecylene.

Especially preferred compounds are those in which B¹ and B² eachindependently represent a group of formula (IV) and A¹ to A⁴ and E¹ toE² each independently represent a group of formula (III).

The invention is particularly useful when the groups of MG¹ and MG² havea mesogenic architecture so that compounds of formula (I) are able to becompatible with a host liquid-crystalline single compound or mixture.Thus preferably at least one of MG¹ and MG² represents a mesogenic groupcomprising at least two optionally-substituted aromatic or non-aromaticcarbocyclic or heterocyclic ring systems.

Preferably one or more of MG¹ and MG² represents a mesogenic groupcomprising 1 to 4 aromatic or non-aromatic carbocyclic or heterocyclicring systems and optionally up to 3 bridging groups. These are morepreferably selected from the meanings of formulae (V):

 C¹-(Z¹-C²)_(a1)-(Z²-C³)_(a2)-(Z³-C⁴)_(a3)  (V)

in which:

-   C¹ to C⁴ are in each case independently optionally-substituted    non-aromatic, aromatic, carbocyclic or heterocyclic groups;-   Z¹ to Z³ are independently from each other —COO—, —OCO—, —CH₂—CH₂—,    —OCH₂—, —CH₂O—, —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single    bond; and-   a1, a2 and a3 are independently integers 0 to 3, such that    a1+a2+a3≦3.

Especially preferred are those in which C¹ to C⁴ are selected from:

with:

-   L being —CH₃, —COCH₃, —NO₂, —CN, or halogen-   u1 being 0, 1, 2, 3, or 4,-   u2 being 0, 1, 2, or 3, and-   u3 being 0, 1, or 2.

More especially preferred are those in which C¹ to C⁴ are selected fromoptionally-substituted cyclohexyl or cyclohexylene, phenyl or phenylene,naphthyl or naphthylene or phenanthryl or phenanthrylene.

For ease of synthesis, the molecules of formula (I) may possess somesymmetrical aspects. These include the following possibilities:

-   n1=n2=1;-   A¹ to A⁴ are identical;-   E¹ and E² are identical;-   MG¹ and MG² are identical;-   CG is a chiral group having at least two chiral centres more    preferably two adjacent chiral centres; or-   B¹ and B² are identical and both consisting of single bonds, oxygen    atoms or an optionally-substituted hydrocarbon group of 1 to 3-C    atoms.

Other aspects of the present invention are

-   a) a liquid crystalline material, especially in the form of a liquid    crystalline mixture, (co)polymer, elastomer, polymer gel or polymer    network, comprising at least two components, at least one of which    is a chiral compound, characterised in that the chiral compound is a    sandwich derivative of formula (I);-   b) a liquid crystalline material, especially in the form of a    cholesteric mixture, or cholesteric polymer network, comprising at    least two components, at least one of which is a chiral compound,    characterised in that the chiral compound is a sandwich derivative    of formula (I);-   c) a cholesteric polymer network obtainable by copolymerisation of    an optically active polymerisable mesogenic mixture comprising:    -   i) at least one chiral or/and achiral nematic polymerisable        mixture chosen from the already reported broad range of chiral        and achiral nematic materials, for example as in Adv. Mater. 5,        107 (1993), Mol. Cryst. Liq. Cryst. 307, 111 (1997), J. Mat.        Chem. 5, 2047 (1995) or in patent publications U.S. Pat. No.        5,593,617; U.S. Pat. No. 5,567,349; GB-A-2297556; GB-A-2299333;        DE-A-19504224; EP-A-0606940; EP-A-0643121 and EP-A-0606939,        optionally selected from EP-A-0606940; EP-A-0643121 and        EP-A-0606939;    -   ii) at least one chiral dopant of formula (I);    -   iii) an initiator;    -   iv) optionally a non-mesogenic compound having at least one        polymerisable functional group, more optionally a diacrylate        compound; and    -   v) optionally a stabiliser;-   d) chiral polymerisable cholesteric mixtures, essentially consisting    of:    -   i) 70 to 99%, preferably 85 to 95% by weight of at least one        achiral polymerisable liquid crystal;    -   ii) 0.1 to 30%, preferably 1 to 15% by weight of a chiral        compound of formula I;    -   iii) 0.1 to 5%, preferably 0.2 to 2% by weight of a        photoinitiator; and    -   iv) 0 to 5%, preferably 0.1 to 1% of a stabiliser; and-   e) a cholesteric film obtainable by the steps comprising ordering    the above mixture in the monomeric state and in situ UV    polymerisation of the resulting ordered mixture.

The invention also includes:

-   a) the use of the compounds as dopants for liquid crystals;-   b) the use of the compounds or liquid crystalline materials for    manufacturing a polymeric cholesteric layer; and-   c) the use of the cholesteric polymer network, chiral polymerisable    cholesteric mixtures, or cholesteric film, in optical components    such as optical filters and polarisers, and especially colour    filters, optical pass band filters, solid state cholesteric filters    for projection displays and circular polarisers.

The compounds of the invention may be readily prepared using methodsthat are well known to the person skilled in the art, such as thosedocumented in Houben-Weyl, Methoden der Organischen Chemie,Thieme-Verlag, Stuttgart. The compounds may for example be madeaccording to the following reaction schemes:

EDC: N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride, DMAP:N,N-Dimethylaminopyridine; DMF: N,N-Dimethylformamide

According to the synthetic ways drawn in Schemes 1-3 typical examplesrepresenting polymerisable chiral “sandwich” derivatives shown in thefollowing list of compounds are prepared. This list is, however, to beunderstood only as illustrative without limiting the scope of thepresent invention:

EXAMPLE 1 DiisopropylL-2,3-bis-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyloxy}-succinate

A solution of mesyl chloride (4.23 g, 36.94 mmol) in 10 ml of dry THFwas added dropwise under argon over a period of 15 minutes to a cooled(−25° C.) solution of 4-(6-acryloyloxyhexyloxy)benzoic acid andtriethylamine (20 ml) in 80 ml of dry THF. The reaction mixture was thenstirred for 60 min at −25° C., treated with a solution of2,5-dihydroxybenzaldehyde (2.3 g, 16.65 mmol) in 60 ml of dry THFcontaining 195 mg of DMAP and further stirred at −25° C. for 2 h. Thereaction mixture was then allowed to warm to room temperature andstirring was continued overnight. The reaction mixture was then pouredinto 120 ml of saturated NaHCO₃ and extracted with 2×200 ml of ether.The combined organic extracts were washed with 3N HCl (200 ml) andsemi-saturated NaCl solution (2×100 ml), dried over MASO₄, filtered anddried to give a slightly yellow pasty material. This was purified byflash chromatography over a short silica column (CH₂Cl₂/Et₂O : 19.5/0.5)to give a white residue (9.25 g) which was dissolved in CH₂Cl₂ (25 ml)then recrystallised from ethanol (250 ml) to give pure2,5-di-[4-(6-acryloyloxy-hexyloxy)benzoyloxy]benzaldehyde as a whitecrystalline material. Yield 8.5 g.b) 2,5-Di-[4-(6-acryloxyhexyloxy)benzoyloxy]benzoic acid

Jones oxidant (CrO₃/H₂SO₄/H₂O) (48 ml) was added to a ice-cooledsolution of 2,5-di-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzaldehyde(8.24 g, 12 mmol) in acetone (300 ml) in a dropwise fashion over aperiod of 30 min. The reaction mixture was stirred overnight at roomtemperature. The resulting green-orange mixture was filtered off toleave a green precipitate that was washed with 600 ml of ether. Thecombined organic solutions were washed with water until the orangecoloration disappeared (6×250 ml). The colourless organic solutionobtained was washed with saturated NaCl solution (2×300 ml), dried overMgSO₄ and filtered. Removal of the solvent gave pure2,5-di-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoic acid as a whitecrystalline material. Yield 8.5 g.

c) DiisopropylL-2,3-bis-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyl-oxy}succinate

A solution of mesyl chloride (1.10 ml) in 5 ml of dry THF is dropwiseadded to a solution of2′,5′-bis-[2,5-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)]benzoic acid (10g) and triethylamine (19.8 ml) in 125 ml of dry THF, cooled at −25° C.and maintained and under argon atmosphere. After complete addition (15min), the reaction mixture is further stirred for 120 min at −25° C.then treated with a solution of diisopropyl L-tartrate (1.35 g) in 20 mlof dry THF containing 695 mg, of DMAP and the reaction mixture isfurther stirred at −25° C. for 2 h. The temperature is then allowed toreach room temperature and stirring is continued overnight. The reactionmixture is filtered over Celite and evaporated to dryness to afford aslightly beige pasty material. This is then flash chromatographed over asilica column affording pure diisopropylL-2,3-bis-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyloxy}succinate [the “L” indicating the formal derivation of the compound fromdiisopropyl L-tartrate] as a transparent oily material which becomespasty upon standing.

Yield: 5.0 g.

EXAMPLE 2 DiisopropylD-2,3-bis-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyloxy-succinate

Following the procedure described in Example 1(C), the reaction wasperformed with 10 g of2′,5′-bis-[2,5-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)]benzoic acid,1.10 ml of mesyl chloride , 19.8 ml of triethylamine, 1.5 g ofdiisopropyl L-tartrate and 695 mg of DMAP to afford, after flashchromatography over a silica column, pure diisopropylD-2,3-bis-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyloxysuccinate[the “D” indicating the formal derivation of the compound fromdiisopropyl D-tartrate] as a transparent oily material which becomespasty upon standing.

Yield: 6.3 g.

EXAMPLE 3O,O-Di-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyl}-1,4,3,6-dianhydro-D-mannitol

Following the procedure described in Example 1(C), the reaction wasperformed with 1.5 g of2′,5′-bis-[2,5-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)]benzoic acid,0.17 ml of mesyl chloride, 3 ml of triethylamine, 0.14 g of1,4,3,6-dianhydro-D-mannitol and 61 mg of DMAP in 50 ml of THF toafford, after flash chromatography over a silica column, pureO,O-di-{2,5-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzoyl}-1,4,3,6-dianhydro-D-mannitolas white crystalline material.

Yield: 0.28 g.

EXAMPLE 4

A mixture is formulated consisting of1% by weight of

and99% by weight of

This mixture forms a cholesteric phase with a pitch of p=4 μm.

1. A compound of formula I:

in which: A¹ to A⁴ each independently represent hydrogen; anoptionally-substituted methyl group; or an optionally-substitutedhydrocarbon group of 2 to 80 C-atoms, in which one or more C-atoms maybe replaced by a heteroatom, in such a way that oxygen atoms are notlinked to one another, selected from formula (II):P-(Sp¹)_(k1)−(X¹)_(t1)−  (II) wherein: P is hydrogen or a polymerisablegroup selected from groups comprising CH₂═CW—, CH₂═CW—O—, CH₂═CW—COO—,CH₂═C(Ph)—COO—, CH₂CH—COO—Ph—, CH₂CW—CO—NH—, CH₂═C(Ph)—CONH—,CH₂═C(COOR′)—CH₂—COO—, CH₂═CH—O—, CH₂═CH—OOC—, (Ph)—CH═CH—,CH₃—CH═N—(CH₂)_(m3), HO—, HS—, HO—(CH₂)_(m3)—, HS—(CH₂)_(m3)—,HO(CH₂)_(m3)COO—, HS(CH₂)_(m3)COO—, HOC(O)—, CH₂═CH—Ph—(O)_(m4)

 wherein: W represents H, F, Cl, Br or I or a C₁₋₅ alkyl group: m3 is aninteger having a value of from 1 to 9; m4 is an integer having a valueof 0 or 1, R′ represents a C₁₋₅ alkyl group; and R″ represents a C₁₋₅alkyl group, methoxy, cyano, F, Cl, Br or I; Sp¹ represents anoptionally-substituted C₁₋₂₀ alkylene group, in which one or moreC-atoms may be replaced by a heteroatom; k¹ is an integer having a valueof from 0 to 4; X¹ represents —O—, —S—, —NH—, N(CH₃)—, —CH(OH)—, —CO—,—CH₂(CO)—, —SO—, —CH₂(SO)—, —SO₂—, —CH₂(SO₂)—, —COO—, —OCO—, —OCO—O—,—S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—, —CH₂—CH₂—, —OCH₂—, —CH₂O—, —CH═CH—,or 13 C≡C—; and t¹ is an integer having a value of 0 or 1: wherein theterm Ph denotes phenylene and (Ph) denotes phenyl; E¹ and E² eachindependently represent hydrogen; an optionally-substituted methylgroup; or an optionally-substituted hydrocarbon group of 2 to 80C-atoms, in which one or more C-atoms may be replaced by a heteroatom,in such a way that oxygen atoms are not linked to one another, selectedfrom formula (II):P-(Sp¹)_(k1)(X¹)_(t1)—  (II) B¹ and B² each independently represent agroup of formula (IV):(X²)_(t2)-(Sp²)_(k2)-(X³)_(t3)  (IV)  wherein: Sp² represents a C₁₋₂₀alkylene group; X² and X³ each independently represent —O—, —S—, —NH—,N(CH₃)—, —CH(OH)—, —CO—, —CH₂(CO)—, —SO—, —CH₂(SO)—, —SO₂—, —CH₂(SO₂)—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—, —CH, —CH₂—,—OCH₂—, —CH₂O—, —CH═CH—, —C≡C— or a single bond; k2 is an integer,having a value of 0 or 1; and t² and t³ are integers, each independentlyhaving a value of 0 or 1; with the proviso that oxygen atoms are notlinked one to another; MG¹ and MG² each independently represent anoptionally-substituted aromatic or non-aromatic carbocyclic orheterocyclic ring system, with 1 to 80 C-atoms with a mesogenicarchitecture; CG is a chiral group having at least two chiral centers,derived from a sugar, from an optically active biaryl group, or from abifunctional or polyfunctional compound comprising an optically activealcohol, glycol, or amino acid; and n1 and n2 are each independently 1or 2, where “n1=2”, or “n2=2”, indicates the presence of two separatelinkages via the groups B^(1,) or the groups B^(2,) between the groupsMG¹ and CG, or CG and MG²; and in which further the substructuresA¹-MG¹-A² and A³-MG²-A⁴ are rod-like shaped organic residues and eachhave a longitudinal axis and are linked lateral to the said longitudinalaxis to B¹ and B², respectively.
 2. A compound as claimed claim 1 inwhich:n1=n2=1.
 3. A compound as claimed in claim 1, in which at least one ofA¹ to A⁴, E¹ and E² includes a polymerisable group.
 4. A compound asclaimed in claim 1, in which one or more of CH₂ groups present in thehydrocarbon chain of the optionally-substituted C₁₋₂₀ alkylene group Sp¹is replaced, independently, by one or more groups selected from —O—,—S—, —NH—, N(CH₃)—, —CH(OH)—, —CO—, —CH₂(CO)—, —SO—, —CH₂(SO)—, —SO₂—,—CH₂(SO₂)—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—,—C≡C—, —(CF₂)—_(r), —(CD₂)_(s)— or C(W¹)═C(W²)—, with the proviso thatno two oxygen atoms are directly linked to each other, wherein W¹ and W²each represent, independently, H, H—(CH₂)_(q1)— or Cl and the integersr, s and q1 each independently represent a number of between 1 and 15.5. A compound as claimed in claim 1, in which A¹ to A⁴ and E¹ to E² eachindependently represent a group of formula (III):P²-Sp⁵-X⁴-  (III) wherein: P² represents hydrogen, CH₂═CW⁵— orCH₂═CW⁵—(CO)_(v2)O—,

 wherein: W⁵ represents H, CH₃, F, Cl, Br or I; and v2 is 0 or 1, R′represents a C₁₋₅ alkyl group; and R″ represents a C₁₋₅ alkyl group,methoxy, cyano, F, Cl, Br or I; Sp⁵ represents a C₁₋₂₀ straight-chainalkylene group; and X⁴ represents —O—, —CO—, —COO—, —OCO—, —C≡C—, or asingle bond.
 6. A compound as claimed in claim 1, in which B¹ and B²each independently represent a group of formula (IV), wherein: X² to X³each independently represent —O—, —CO—, —COO—, —OCO—, —C≡O—, or a singlebond; and Sp² represents a C₁₋₂₀ straight-chain alkylene group.
 7. Acompound as claimed in claim 1, in which at least one of MG¹ and MG²represents a mesogenic group comprising at least twooptionally-substituted aromatic or non-aromatic carbocyclic orheterocyclic ring systems.
 8. A compound as claimed in claim 1, in whichone or more of MG¹ and MG² represents a mesogenic group comprising 1 to4 aromatic or non-aromatic carbocyclic or heterocyclic ring systems andoptionally up to 3 bridging groups.
 9. A compound as claimed in claim 8,in which MG¹ and MG² are selected from the meanings of formulae (V):C¹-(Z¹-C²)_(a1)-(Z²-C³)_(a2)-(Z³-C⁴)_(a3)  (V) in which: C¹ to C⁴ are ineach case independently optionally-substituted non-aromatic, aromatic,carbocyclic or heterocyclic groups; Z¹ to Z³ are independently from eachother —COO—, —OCO—, —CH₂—CH₂—, —OCH₂—, —CH₂O—, —CH═CH—, —C≡C—,—CH═CH—COO—, —OCO—CH═CH— or a single bond; and a1, a2 and a3 areindependently integers 0 to 3, such that a1+a2+a3≦3.
 10. A compound asclaimed in claim 9, in which C¹ to C⁴ are selected from:

with: L being —CH₃, —COCH₃, —NO₂, —CN, or halogen u1 being 0, 1, 2, 3,or4, u2 being 0, 1, 2, or 3, and u3 being 0, 1, or
 2. 11. A compound asclaimed in claim 10, in which C¹ to C⁴ are selected fromoptionally-substituted cyclohexyl or cyclohexylene, phenyl or phenylene,naphthyl or naphthylene or phenanthryl or phenanthrylene.
 12. A compoundas claimed in claim 1, in which A¹ to A⁴ are identical.
 13. A compoundas claimed in claim 1, in which E¹ and E² are identical.
 14. A compoundas claimed in claim 1, in which MG¹ and MG² are identical.
 15. Acompound as claimed in claim 1, in which CG is a chiral group having atleast two adjacent chiral centers.
 16. A compound as claimed in claim 1,in which B¹ and B² are identical and both consisting of single bonds,oxygen atoms or an optionally-substituted hydrocarbon group of 1 to 3-Catoms.
 17. A liquid crystalline material, in the form of a liquidcrystalline mixture, (co)polymer, elastomer, polymer gel or polymernetwork, comprising at least two components, at least one of which is achiral compound, characterised in that the chiral compound is a compoundof formula (I) as claimed in claim
 1. 18. A liquid crystalline material,in the form of a cholesteric mixture, or cholesteric polymer network,comprising at least two components, at least one of which is a chiralcompound, characterised in that the chiral compound is a compound offormula (I) as claimed in claim
 1. 19. A cholesteric polymer networkobtainable by copolymerisation of an optically active polymerisablemesogenic mixture comprising: i) at least one chiral or/and achiralnematic polymerisable mixture chosen from chiral and achiral nematicmaterials; ii) at least one chiral dopant of formula (I) as claimed inclaim 1; iii) an initiator; iv) optionally a non-mesogenic compoundhaving at least one polymerisable functional group; and v) optionally astabilizer.
 20. A chiral polymerisable cholesteric mixture, essentiallyconsisting of: i) 70 to 99% by weight of at least one achiralpolymerisable liquid crystal; ii) 0.1 to 30% by weight of a chiralcompound of formula I as claimed in claim 1 iii) 0.1 to 5% by weight ofa photoinitiator; and iv) 0 to 5% of a stabiliser.
 21. A cholestericfilm obtainable by the steps comprising ordering a chiral polymerisablecholesteric mixture as claimed in claim 20 in the monomeric state and insitu UV polymerisation of the resulting ordered mixture.
 22. A compoundas claimed in claim 5, wherein Sp⁵ represents ethylene, propylene,butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene,undecylene, or dodecylene; and X⁴ represents —O—, —COO—, —OCO— or singlebond.
 23. A compound as claimed in claim 6, wherein X² to X³ eachindependently represent —O—, —COO—, —OCO— or a single bond; and Sp²represents ethylene, propylene, butylene, pentylene, hexylene,heptylene, octylene, nonylene, decylene, undecylene or dodecylene.
 24. Acholesteric polymer network as claimed in claim 19, wherein thenon-mesogenic compound having at least one polymerisable functionalgroup is a diacrylate compound.
 25. A method which comprises adding acompound as claimed in claim 1 as a dopant to liquid crystals or to amixture of liquid crystals.
 26. A method which comprises ordering aliquid crystalline material as claimed in claim 17 in the monomericstate and in situ UV polymerizing the ordered mixture to produce apolymeric cholesteric layer.
 27. A method which comprises ordering aliquid crystalline material as claimed in claim 18 the monomeric stateand in situ UV polymerizing the ordered mixture to produce a polymericcholesteric layer.
 28. An optical component comprising a cholestericpolymer network as claimed in claim
 19. 29. An optical componentcomprising a chiral polymerizable cholesteric mixture as claimed inclaim
 20. 30. An optical component comprising a cholesteric film asclaimed in claim 21.